We make a judgment on our preference concerning foods or farm products based on many elements, such as taste, smell and color. Among various elements we rely on as the basis for our judgment on preference, food texture is an especially important element. Such a food texture derives from mechanical characteristics (primarily elasticity or viscosity) of a food. Consequently, by measuring the elasticity or viscosity of a food, it should become possible to quantify the food texture. For example, a material testing machine has been disclosed, which quantifies customarily used food textures, such as “stickiness” or “al dente”, by measuring mechanical characteristics of a food for a test sample, such as noodle or pasta (for example, see Patent Literature 1). By the material testing machine, a test sample such as noodle is thrust by a plunger to a constant distance and the plunger is retreated to a point where a stress (resilient force) given by the test sample on the plunger becomes zero, to obtain a curve showing the relationship between the retreated distance and the thrust load. And from the area of the region formed by the curve the repulsion energy inherent to the test sample is calculated and the “stickiness” or “al dente” of the test sample is quantified.
Food texture is however not limited to “stickiness” or “al dente”. For example, a “crisp” texture in masticating fresh cucumber or celery, or a “creamy” texture of a ripe pear stimulates our appetite greatly. Since such food textures cannot be expressed by mechanodynamic measurements, for example, by a conventional rheometer, they have been always evaluated solely by a sensory evaluation (a test depending on human sense).
Further, a system for quantifying a “crunchiness” of a dry and porous food, such as a cookie or a snack, namely crispness, has been also disclosed recently (for example, see Patent Literature 2). According to the system, a rupture curve is determined by measurements, a frequency analysis is conducted for the determined rupture curve to determine rupture energy in a predetermined frequency region, and the crispness is quantified by the rupture energy.
Further, a food texture measuring apparatus has been disclosed that quantifies food textures such as a “crisp feeling” of a food irrespective of the water content (for example, see Patent Literature 2). According to the food texture measuring apparatus a probe is inserted into a food at a predetermined velocity, from signals outputted from a piezoelectric element connected with the probe the peak number of pulses per unit time is calculated, and the food texture is determined quantitatively by the peak number of pulses.
Further, a food texture measurement method for quantifying a “crisp feeling” and a “crunchiness” of a food has been disclosed (for example, see Patent Literature 4). According to the food texture measurement method, a probe is inserted into a food at a predetermined velocity, signals of a plurality of frequency bands are extracted from signals outputted from a piezoelectric element connected with the probe, and the amplitude density per unit time of the signals of each frequency band is determined as an index of a food texture of the food.